"I believe that whatever the merits of Brexit may be in the UK, that's a domestic debate here, I think it offers greater opportunities for Australia in the UK than ever," he said.

"I can assure you that we will do everything we can to enable the UK to enter into the most favourable, open, to quote President Trump, fair and reciprocal, trade deal between Australia and the UK.

Malcolm Turnbull said the UK under Mrs May would be more global and open to trade.

"We want an absolute level paying field.

"And why wouldn't we? Because we think, by and large, as long as there is a level playing field we can always be competitive with the Poms."

Mr Turnbull used the speech to repeat his familiar refrain warning against a retreat towards protectionism, like that happening in the United States under Donald Trump.

"Look, the reality is we are enjoying, at the moment in Australia, very strong jobs growth, very strong investment growth. We do not accept the lure of protectionism," he said.

"We know that the strong jobs growth we're enjoying in Australia is in large measure because of trade, and we do everything we can to open up more markets for more Australians to invest, to trade, to export, to do all things that you're doing."

Before leaving the UK overnight Saturday AEST, Mr Turnbull was scheduled to hold a meeting with British Prime Minister Theresa May about issues of cybersecurity – particularly in relation to Russia.

The two leaders were expected to discuss and formalise work on detecting, preventing, mitigating and responding to cyber attacks, whether from terrorists, criminal syndicates, states or state sponsored actors.

The work represents a new era of proactive, collaborative measures that strengthen cyber security and counter foreign interference.

The pair were also expected to discuss free trade.

Mr Turnbull said the UK under Prime Minister May would be more global and open to trade, and "once again become a nation that looks to the whole world, and not just Europe."

​After four days in London for the Commonwealth Heads of Government Meeting, Mr Turnbull will now travel to Germany where he and Chancellor Angela Merkel are expected to discuss cybersecurity and China, as well as mount a case against protectionism.